Thermally processable imaging elements, including films and papers, are well known. These elements include photothermographic elements in which an image is formed by imagewise exposure of the element to light followed by development involving uniformly heating the element. These elements also include thermographic elements in which an image is formed by imagewise heating the element. Such elements are described in, for example, Research Disclosure, June 1978, Item No. 17029 and U.S. Pat. Nos. 3,080,254, 3,457,075 and 3,933,508.
Polyester materials are widely used as a support or base for such photothermographic or thermographic materials, on account of their excellent physical properties for that purpose.
If the adhesion between the photothermographic layer and the support is insufficient, several practical problems arise. If the photographic material is brought into contact with a sticky material, such as splicing tape, the photographic layers may be peeled from the support resulting in a loss of image-forming capability. In the manufacturing process, a photographic subjected to slitting or cutting operations and in many cases perforated holes are punched into the material for film advancement in cameras and processors. Poor adhesion can result in a delamination of the photographic layers from the support at the cut edges of the photographic material which can generate many small fragments of chipped-off emulsion layers which then cause spot defects in the imaging areas of the photographic material. If there is poor adhesion between the emulsion and base, delamination of the emulsion from the base may occur during thermal development of the photographic material in the processors. The photographic material may undergo spot delamination or blistering due to processing at elevated temperatures or may be damaged by transport rollers during processing or subsequent thereto.
Another variation on this problem is "blocking," which occurs during the manufacturing of a photographic element when a continuous web coated with a subbing layer is wound in roll form before application of the emulsion layers. In this instance, the front-side containing the subbing layer is brought into intimate contact with the backside layers, which then can stick or block together. This prevents or makes more difficult the unwinding of the roll for subsequent coatings and can also cause static build-up in the roll, leading to charging or marking of the emulsion layer.
In traditional (non-photothermographic) systems, various subbing processes and materials have, therefore, been used or proposed in order to produce improved adhesion between the support film and the hydrophilic colloid layer in traditional silver-halide photographic systems. Polymers known and used in what is referred to as a subbing layer for promoting adhesion between a support and an emulsion layer are disclosed in U.S. Pat. Nos. 2,627,088; 2,968,241; 2,764,520; 2,864,755; 2,864,756; 2,972,534; 3,057,792; 3,071,466; 3,072,483; 3,143,421; 3,145,105; 3,145,242; 3,360,448; 3,376,208; 3,462,335; 3,475,193; 3,501,301; 3,944,699; 4,087,574; 4,098,952; 4,363,872; 4,394,442; 4,689,359; 4,857,396; British Patent Nos. 788,365; 804,005; 891,469; and European Patent No. 035,614. Often used are polymers of monomers having polar groups in the molecule such as carboxyl, carbonyl, hydroxy, sulfo, amino, amido, glycidyl or acid anhydride groups, for example, acrylic acid, sodium acrylate, methacrylic acid, itaconic acid, crotonic acid, sorbic acid, itaconic anhydride, maleic anhydride, cinnamic acid, methyl vinyl ketone, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxychloropropyl methacrylate, hydroxybutyl acrylate, vinylsulfonic acid, potassium vinylbenezensulfonate, acrylamide, N-methylamide, N-methylacrylamide, acryloylmorpholine, dimethylmethacrylamide, N-t-butylacrylamide, diacetonacrylamide, vinylpyrrolidone, glycidyl acrylate, glycidyl methacrylate, or copolymers of the above monomers with other copolymerizable monomers.
Additional examples are polymers of ethylenically unsaturated esters or ethylenically unsaturated acids represented by, for example, acrylic acid esters such as ethyl acrylate or butyl acrylate, methacrylic acid esters such as methyl methacrylate or ethyl methacrylate, or copolymers of these monomers with other vinylic monomers; or copolymers of polycarboxylic acids such as itaconic acid, itaconic anhydride, maleic acid or maleic anhydride with vinylic monomers such as styrene, vinyl chloride, vinylidene chloride or butadiene, or trimers of these monomers with other ethylenically unsaturated monomers.
Traditionally, one commonly practiced process for providing good adhesion of photographic emulsions to polyester supports involves applying an adhesion promoting layer or subbing layer to the polyester followed by a coating of gelatin. Materials in the adhesion promoting layer generally comprise a copolymer containing a chloride group such as vinylidene chloride.
Although apparently experiencing little commercial use, glycidyl-containing polymers have been proposed for improving the adhesion of a traditional light-sensitive emulsion to a polyester support. For example, U.S. Pat. No. 4,328,283 to Nakadata et al. discloses a polyester support on the surface thereof with a subbing layer formed by coating the support surface with an aqueous composition containing a copolymer consisting of the following components: (1) 30-70 wt % glycidyl acrylate and/or glycidyl methacrylate monomer, (2) 3-45 wt % hydroxyalkyl acrylate having an alkyl group of 2 to 4 carbon atoms and/or hydroxyalkyl methacrylate monomer, and (3) 0-67 wt % copolymerizable vinyl monomer. It was found that wet-film adhesion force was low in the case when less than 30 wt % of the first component was present, and dry-film adhesion force deteriorated when more than 70 wt % was present.
U.S. Pat. No. 3,645,740 to Nishio describes photographic elements that use a blend of gelatin with either a glycidyl methacrylate or glycidyl acrylate homopolymer or copolymer as subbing layers for PET (polyethylene terephthalate) supports. Besides providing adhesion, the coating solutions were found to have good stability, and wound coated rolls did not block.
U.S. Pat. No. 4,098,952 to Kelly et al describes a primer for PET supports that contains a copolymer comprising 3-25 mole % glycidyl (meth)acrylate. U.S. Pat. No. 4,128,426 to Ohta et al describes a subbing layer for photographic film which comprises a copolymer containing 20 to 90% glycidyl (meth)acrylate. U.S. Pat. No. 4,609,617 to Yamazaki et al describes a subbing layer for photographic film comprising a copolymer containing 0.01 % to 70% glycidyl (meth)acrylate. GB 1583343 to Mann describes a subbing layer for photographic elements that contains copolymers of acrylic acid or methacrylic acid and their derivatives such as glycidyl (meth)acrylate. GB 2037792 to Kitihara et al describes subbing layers for photographic polyester supports that use copolymers containing 35-55 wt % glycidyl (meth)acrylate. The subbing layer is applied during the manufacturing of the PET. The applied subbing layer is then subjected to corona discharge treatment before applying additional layers. Other patent publications which disclose, in general, the use of a copolymer containing glycidyl methacrylate as a subbing layer for photographic use include JP 5134356, JP 59094756, and EP 35614. A research disclosure, RD 18358 1979, describes the use of a butyl acrylate-glycidyl methacrylate-styrene (40-40-20) copolymer as a subbing layer for photography. Notwithstanding the above disclosures, subbing layers comprising polymers of glycidyl acrylic or glycidyl methacrylate, and particularly homopolymers of these monomer, have not experienced widespread commercial application, suggesting that such proposed subbing materials and processes are either not economical, difficult to manufacture, and/or do not provide the desired performance characteristics for commercial application.
The latter glycidyl-containing polymers have been disclosed for use in traditional photography. More commonly, however, traditional methods to improve adhesion of the emulsion have included vinylidene-chloride-containing copolymers as subbing layers and surface treatment. For photothermographic systems, however, these approaches have been found to alter the emulsion sensitometry/keeping, cause blocking of support rolls (before emulsion coating), or provide inadequate adhesion.
Thermally processable imaging elements which include a thermographic or photothermographic layer, a protective overcoat layer and an adhesive interlayer, comprising a glycidyl-containing polymer, interposed between the overcoat layer and the thermographic or photothermographic layer are disclosed and claimed in U.S. Pat. No. 5,422,234. This patent discloses a polymer having glycidyl-functionality which polymer has been found to serve as an effective adhesion-promoting layer that overcomes the difficult problem of providing good adhesion between an overcoat that is typically hydrophilic and an imaging layer that is typically hydrophobic. Moreover, use of a polymer having glycidyl functionality for this purpose not only provides effective overcoat/imaging layer adhesion, but causes no adverse sensitometric effects and involves the use of low cost, readily available materials which are easily handled and coated and are environmentally advantageous.
None of the above prior art discloses the use of glycidyl-functional polymeric layer between a polyester support and a poly(vinyl acetal)-containing phothermographic or thermographic imaging layer to promote adhesion. In this case, the imaging layer is applied, not in an aqueous system, but in an organic solvent.
It is accordingly a primary object of the present invention to provide subbed polyester supports for excellent film adhesion to a poly(vinyl acetal)-containing layer.